Packing containers of the type described in EPO Pat. No. 19324, to which reference is made, are manufactured from a flexible packing laminate which comprises different material layers, generally a central carrier layer of paper which is enclosed on both sides by homogeneous plastic layers of thermoplastic material, e.g. polyethylene. The packing laminate is converted by folding and heat-sealing in a known manner to packing containers which are filled with contents, e.g. milk, juice or the like. To allow consumption of the contents of the packing containers the latter are provided with some form of opening arrangement, e.g. a tearing indication or a pouring opening with a tear-off cover strip. In order to prevent spillage of contents when the packing container is opened, the packing container is filled with a slightly smaller amount of contents than what is theoretically possible. This is achieved by making the flexible walls of the packing container curve somewhat inwards when the packing container is completely filled and closed, and in connection with the opening of the packing container air will be sucked in through the opening at the same time as the flexible walls revert to a plane or slightly outwards curved position, and the liquid level will thereby drop. In spite of this a certain spillage occurs occasionally, since the sudden lowering of the liquid level causes spattering from the exposed pouring opening.
The abovementioned inconveniences can be avoided by filling the packing container with a smaller quantity of liquid and thus providing it with so-called headspace, that is to say an air-filled or gas-filled space between the product and the top side of the packing container, which to a certain extent prevents spatter and spillage on opening. However, it is desirable, if possible, to avoid headspace, since this naturally involves an increase in packing material consumption which is not matched by any increase in the volume of packed contents. With certain products it is, moreover, a disadvantage if air is present in the package, and the air has to be replaced, therefore, by some inert gas which complicates the packing process and makes it more expensive